Modeling Cassegrain Antenna Ka Band

Abstract

As frequency increases wavelength decreases. Hence it becomes possible to construct antennas that are of moderate physical size. This allows the possibility of constructing antennas with a large aperture, high gain and narrow beamwidth. This type of radiation behaviour allows the antenna to be deployed in point to point microwave links. A very convenient way of achieving this behaviour at microwave frequencies is to use shaped metal reflectors. This method use Cassegrain design for subreflector configuration where the subreflector is a section of hyperboloid within the focus of the paraboloidal main reflector. The subreflector has two focal points. One of which is made to coincide with that of the main reflector and the other with the phase center of the feed horn. To facilitate maintenance it is possible to install it at ground level in a building under the antenna by using a system of microwave mirrors to guide the radio waves from the primary feed at ground level to the focus of the reflector. This arrangement permits the high power and low noise amplifiers to be installed at the ground surface. A rotary joint is not required because the beams are guided in free space rather than via waveguide. The perturbation caused by the auxiliary mirror leads to a slight reduction of gain.